Construction machines, particularly bulldozers, are mainly used in earth work on irregular ground. Therefore, the bodies of construction machines are subject to large vibrations during movement, and as a result the operators suffer from substantial fatigue. For this reason, it is desirable, wherever possible, to relieve the effects of the machine vibrations on the operators.
As shown in FIG. 14, a body vibration mode of a bulldozer is such that a horizontal transversal axis X, a horizontal longitudinal axis Y, and a vertical axis Z, all of which pass through the center of gravity G of a bulldozer 100, denote pitching, rolling, and yawing, respectively.
FIG. 15 is a partial side view illustrating a floor frame supporting structure for an operator cabin on a conventional bulldozer, and FIG. 16 is a rear view as viewed in the direction of arrow D in FIG. 15. Brackets 31L and 31R are provided at the front left portion and the front right portion, respectively, of the operator cabin 30, while brackets 32L and 32R are provided at the rear left portion and rear right portion, respectively, of the operator cabin 30. The front brackets 31L and 31R are coupled to rubber mounts 40L and 40R which are mounted on the brackets 34L and 34R, which in turn are fixed to a front part of the vehicle body frame 33. The rear brackets 32L and 32R are coupled to rubber mounts 39L and 39R which are mounted on brackets 35L and 35R, which in turn are fixed to a rear part of the vehicle frame 33.
FIG. 17 is a sectional view of the front left side rubber mount 40L, taken along sectional line E--E in FIG. 15. The construction of the front right side rubber mount 40R and that of the rear right side and rear left side rubber mounts 39R and 39L is the same as that of the front left side rubber mount 40L. A block 42L, in which a pipe 43L is closely mounted, is encased in a rubber member 44L which is housed in a case 41L, and a cover 45L is clamped to the case 41L by bolts 46L, thus forming the rubber mount 40L. The case 41L is clamped to a vehicle body frame bracket 34L by bolts 48L, and is pivotally coupled with a bracket 31L on the operator cabin 30 by a bolt 47L which is positioned concentrically within pipe 43L and extends through the opposite walls of cabin bracket 31L. The vibration of the machine body is absorbed by the deflection of the rubber member 44L and its counterparts in the other rubber mounts 39R, 39L, and 40R.
The above supporting member involves a problem in that, since a vibration of the machine body is absorbed only by deflection of the rubber members 44 in the rubber mounts 39L, 39R, 40L, and 40R, a vibration due to a large shock, such as is caused when the machine vehicle runs over an obstruction, cannot be sufficiently absorbed.
Therefore, a supporting structure as shown in FIGS. 18 and 19 has been contrived. Specifically, a front right side portion and a front left side portion of the floor frame 51 of the operator cabin 50 are secured to pins 54L and 54R, respectively, which are pivotally mounted by rubber bushings in brackets 53L and 53R, which are fixed to the vehicle body frame 52. A rear left side portion and a rear right side portion of the floor frame 51 are coupled by suspension cylinders 60L and 60R, respectively, to brackets 55L and 55R, which are fixed to the vehicle body frame 52.
FIG. 20 is an enlarged sectional view of the rear left side suspension cylinder 60L, the rear right side suspension cylinder 60R having the same construction. A cylinder body 61L has an upper chamber 62L and a lower chamber 63L, which are separated by a partition 64L having an orifice 65L such that the orifice 65L provides restricted communication between the two chambers. The chambers 62L and 63L are sealed with oil. A piston 71L is fixed to a rod 70L and is inserted into the lower chamber 63L for reciprocating movement therein along the longitudinal axis of the lower chamber 63L. The piston 71L is provided with an orifice 72L which provides restricted fluid communication between the portions of lower chamber 63L on opposite sides of the piston 71L. A spring 73L is positioned about the rod 70L between the piston 71L and the partition 64L to resiliently bias the piston 71L downwardly. The cylinder body 61L is clamped to the cabin floor 51 by a bolt 66L, while the distal end of the rod 70L is clamped to a first rear body frame bracket 55L by a nut 74L.
The spring 73L in the suspension cylinder 60L supports the left rear part of the operator cabin 50 at a steady state condition in which a sufficient stroke of the piston 71L is reserved. When a vertical load is applied, oil in the lower chamber 63L above the piston 71L is pressurized and a portion of the pressurized oil is forced through the orifices 65L and 72L to produce a damper effect. Accordingly, when a large load is applied to the machine vehicle in the vertical direction, the operator cabin 50 pitches around the longitudinal axis of pins 54L and 54R, as shown by the double headed arrow in FIG. 18, thereby absorbing vibration. Rolling in the horizontal direction is prevented by using the shackle rod 75 to couple the bracket 55L, which is fixed to the vehicle frame 52, and the floor frame 51, with the shackle rod 75 being pivotally mounted at both ends, as shown in FIG. 19.
This supporting structure sufficiently absorbs even a large shock load, such as is caused when the machine vehicle runs over an obstruction, and also prevents rolling of the cabin. However, this supporting structure involves a problem in that the construction is complex due to a large number of components and is expensive.